The present invention relates to an inner-focusing high zoom ratio lens, and more particularly, to a high zoom ratio lens that is designed to be downsized and to designate zoom adjusting ranges in a part of a shorter depth of focus.
The prior art inner-focusing high zoom ratio lens has a greater variation in a feeding distance of a focusing lens with respect to the higher close-up point, and when a single focusing cam is provided to magnify a close-up performance, a displacement to focus becomes resultantly increased in the remaining zoom ranges, which leads to a necessity for vari-focal feature. Focusing cam curves used to shift a point of such vari-focal operation to a zoom range require appropriate balance of parameters of zooming and focusing. However, it is difficult to ensure a well-balanced cam configuration to attain smooth zooming and focusing, and hence, a rotation angle of a focusing cam must be altered, or some compensation is required in the focusing cam.
Japanese Patent Laid-Open No. H8-304684 discloses a high zoom ratio lens in which a focusing lens moves forward and backward while simultaneously moving in a circumferential direction during either zooming or focusing. A cam configuration is used for a guide groove that urges a focusing cam barrel to circumferentially move while a cam pin fitted in the guide groove moves therein along in the focusing cam barrel, so that a displacement in a circumferential direction distorts an operational range with the focusing cam during zooming so as to attain an appropriate displacement in any of zoom ranges for focusing.
However, it is still difficult to ensure a sufficient displacement to magnify a close-up performance and to attain a displacement for focusing under a restricted condition of shift of focal point in the entire zoom range.
In a high zoom ratio lens disclosed in Japanese Patent Laid-Open No. 2000-89086, a focus compensating cam is disposed in a rotational member along with a focusing cam in order to attain an appropriate displacement to focus. However, since a focus lens in such mechanism is designed to linearly move during zooming, a displacement is fixed in any zoom range, and a sufficient displacement for compensation cannot be ensured to shorten a close-up depth in any zoom range of the high zoom ratio lens.
The present invention is made to overcome the above-mentioned disadvantages in the prior art inner-focusing zoom lens. Accordingly, it is an object of the present invention to provide a high zoom ratio lens that can be configured to be efficiently downsized and to effectively attain sufficient compensation rate for focusing lenses in any type of zoom ranges.
It is another object of the present invention to provide a high zoom ratio lens that can be configured to effectively designate zoom adjusting ranges in a part attaining a shorter depth of focus.
The invention is directed to provide a high zoom ratio lens that can be configured to be efficiently downsized and to effectively attain sufficient compensation rate for focusing a lens component in any type of zoom ranges. The high zoom ratio lens comprises a focusing lens B that moves forward and backward while simultaneously moving in a circumferential direction during zooming and focusing, and a focusing cam barrel 9 that includes a first focusing cam 103 moving the focusing lens B during the focusing, a zooming cam 100 moving the focusing lens B during the zooming, and a second focusing cam 102 compensating for a displacement of the first focusing cam 103 and a telescopic movement of the focusing cam barrel 9 in any of zoom ranges. The high zoom ratio lens further comprises a stud C that is engaged with the zooming cam 100 and moves within a range corresponding to circumferential movement of the first focusing cam 103.